This invention relates to devices used to authenticate currency. More particularly, it relates to verification machines that detect security threads embedded in currency.
The use of security threads embedded in currency paper has increased due to the advent of high-resolution, true-color photocopying machines. If modern currency does not have an embedded security thread, the currency can be more easily duplicated with a color photocopier. When the security thread is embedded, it is harder to illicitly reproduce. Unfortunately, it is also harder to verify by visual inspection. Consequently, various detectors have been invented.
One such security thread verification device is described in U.S. Pat. No. 4,980,569 to Crane et al. This detector and others similar to it require the measurement of the thread properties in the presence of the printed currency paper. The physical properties of the security thread are different than the physical properties of the paper, yet they are difficult to measure due to the interference produced by the surrounding ink.
Detectors in the past have often included capacitors. Unfortunately, these devices are not as successful as originally anticipated. With these capacitor devices, the sensor has to come in contact with the paper immediate to the thread. If the sensor does not come into contact with the paper immediate to the thread, the sensor's ability to detect the thread is reduced, and sometimes nullified. Consequently, to ensure that the thread comes into contact with the sensor, the user or transport is forced to accurately place the currency through the detector. If the user or transport inaccurately places the currency such that the thread does not come into contact with the sensor, the detector does not detect the thread; therefore, it designates the currency as counterfeit. In addition, these capacitance devices are typically very slow in authenticating the presence or absence of the thread. This is undesirable in commercial situations where the processing of large numbers of bills must be done at high rates of speed.
Accordingly, it is the primary object of the present invention to provide an improved security thread detector.
It is a general object to provide a security thread detector that is not affected by a user's or transport's inaccurate placement of the thread within the device.
It is yet another object to provide a detector that works without the need of a sensor coming into contact with the paper immediate to the security thread.
It is still another object to provide a detector that can determine a banknote's authenticity at very fast rates.
It is still a further object to provide a detector that is not hampered by the presence of ink, soil, or general degradation that occurs to currency in circulation.
The above and other objects and advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.